1. Field of the Invention
The present invention is directed generally to a light emitting diode and, in particular, to a light emitting diode for emitting light in the green spectral range.
2. Description of the Related Art
Luminous diodes, or light emitting diodes (also referred to as LEDs) are semiconductor diodes which exhibit a luminescence characteristic, in other words, emitting light in the visible spectral range when current flows in the conducting direction.
It is know that gallium phosphide (GaP) semiconductor substrates are used for the manufacture of light emitting diodes having a purely green luminescence. The layer sequence for generating the light active pn-junction is produced by vapor phase epitaxy or liquid phase epitaxy. The use of liquid phase epitaxy provides a light emitting diode of a higher efficiency.
The known green emitting LEDs are composed of GaP epitaxy wafers which are manufactured with such purity and doping that they emit light in the desired, green spectral range on the wafer level. To manufacture what are referred to as pure-green emitting diodes (wherein the dominant wavelength is approximately 557.+-.4 nm) nitrogen inclusion is foregone in the epitaxy method even though a lower efficiency for the LED is a result thereof. The p-doped wafer side of the LED is provided with a partial contact of gold beryllium as one of the two diode contacts in a prescribed surface region. However, beryllium is carcinogenic and extremely toxic. As an accumulatable toxin, it can have a fatal effect due to skin, mucous membrane, and lung disorders.
It is known to provide gold-zinc contacts in green emitting light emitting diodes as the contact for the p-conductive wafers side instead of the gold-beryllium contact. However, this results in an undesired red emission for diodes having such contacts.